The "screen" check box for Project/Job is grayed out when customizing Invoices or Estimates

When attempting to customize transactions such as Invoices or Estimates, the field that allows us to select "Screen" to show Project/Job on the screen is grayed out and cannot be selected.

Why this is happening

This field is populated by the job name found in the Customer:Job field on the upper-left of the Invoice or Estimate form. (e.g. John Smith: Kitchen would print Kitchen in the Project field). Since this field pulls from the actual Job set up under the Customer, it cannot be manually edited on the form.